The present application relates to downhole tools for depth detection in downhole strings and more particularly, depth identification of certain structures in downhole strings. Methods of use are also provided.
A variety of downhole operations require accurate identification of a precise location in a downhole string. Examples of operations that may require a specific location to be identified in a downhole string include perforation operations and cutting or severing operations (e.g. cutting a drill string or production string). Other applications requiring accurate depth identification include wellbore fluid sampling, temperature measurement, and pressure measurements. In some cases, the precision of depth identification required can be as small as around one foot or two feet.
Merely measuring the length of line extended while lowering a tool down a downhole string or pipe is usually insufficient for identifying a precise depth due to the effects of line stretch over long wellbore depths, which, in some cases, may extend several miles into the ground. In some cases, highly deviated wells further complicate measuring the line length deployed downhole. Although the amount of line stretch can be estimated in some circumstances, the uncertainties involved in these methods of estimation are often inadequate and consequently, such methods are often unsuccessful.
To aid in locating a precise location in a downhole string, specially designed spool pieces with internal notches may be installed in the casing string during completion. Because the precise location of the specially designed spool pieces are known with a high certainty, the internal notches of the specially designed spool pieces aid locating tools that are designed to interface with the internal notches of the specially designed spool pieces. Conventional mechanical locating devices, however, suffer from a number of disadvantages. For example, conventional mechanical locating devices, such as communication module (CM) locator tools, often have difficulty traversing various downhole restrictions in the pipe due to the relatively large size of conventional CM locator tools. For example, subsurface safety valves may inhibit the passing of a conventional CM locator tool.
Additionally, conventional mechanical locating devices are designed as engage-once devices, where the device activates once or latches in place at the desired internal notch. After initial deployment, the conventional mechanical locating device is unable to “reset” downhole for locating another desired locating notch or for repeating the same test. To reset such a device for subsequent measurements, operators must retrieve the prior art tool from the wellbore to reset the tool for another engagement or deployment.
In some cases, it may be desired to identify multiple depths in a downhole string or to take multiple loggings at the same depth for verification purposes. Because conventional locating devices are activate-once or engage-once devices incapable of being reset downhole for another activation, they are unsuitable for this purpose.
Another disadvantage of conventional devices are false engagements. This disadvantage is even more pronounced for devices that are limited to one engagement or one deployment per downhole trip because the device must be retrieved before being capable of performing another measurement. Accordingly, improved locating devices are needed to address one or more disadvantages of the prior art.